1. Field of the Invention
The present invention relates to technology for outputting images based on image data, and in particular relates to technology for outputting images by performing specific image processing on image data to generate appropriate dot density.
2. Description of the Related Art
Image output devices for outputting images by forming dots on various types of output media such as a printing medium or liquid crystal display are widely used as output devices for various types of imaging devices. With these image output devices, images are handled in a form divided into minute regions known as pixels, and the dots are formed on these pixels. Where dots are formed on pixels, on the individual pixel level, it is of course only possible for a pixel to assume either a state in which a dot is formed or one in which no dot is formed. However, on the level of an area of certain size, it is possible to produce a higher or lower density of formed dots, making it possible to output multi-tone images by unit of varying the density of the dots formed. For example, when forming dots from black ink on printing paper, areas in which dots are formed densely will appear darker, while conversely areas in which dots are sparse will appear lighter. Where luminescent spot dots are formed on a liquid crystal screen, areas in which dots are formed densely will appear lighter, while areas in which dots are sparse will appear darker. Consequently, appropriate control of density at which dots are formed enables output of multi-tone images. Data for controlling formation of dots so as to give appropriate formation density in this way is created by executing specific image processing on the images for output.
Recent years have seen demand for larger size and higher picture quality in output images from these image outputting devices. With regard to demand for higher picture quality, it is effective to divide images into finer pixels. Making the pixels smaller affords higher picture quality because the dots that make up the images become indiscernible. The demand for larger images is handled by increasing the number of pixels. While it is of course possible to make an output image larger by increasing the size of individual pixels, doing so would lead to a reduction in picture quality, so increasing the number of pixels is an effective response to the demand for larger images.
Naturally, when the number of pixels making up an image is increased, more time is required for image processing, making it difficult to output images quickly. Accordingly, there has been proposed a technology able to perform imaging processing quickly (Japanese Unexamined Patent Application Publication 2002-185789).
However, even where image processing can be performed quickly, time is required for transfer of the original image data, and for transfer of the processed image data, so there is a limit to the effectiveness of the aforementioned technology in speeding up the output of images.
In recent years there has also arisen a demand to be able to take image data shot with a digital camera or the like, and to supply the data directly to a printer or other image output device in order to output an image immediately. In such cases, it is not possible to perform image processing using an image processing device with high processing capability, such as a personal computer. Consequently, there is an increased need for image processing that while simple enough to be performed by a digital camera or other image capture device, an image output device, or jointly between the two, also affords excellent picture quality.